1. Field of the Invention
The present invention relates to the patterning of a metal feature using a metal nanoparticles containing material and exposing it to radiation.
2. Discussion of the Background
Currently available technology for the micro fabrication of metal patterns includes:
1) use of masks to define patterns of metal by deposition or etching (Shacham-Diamand, Y., Inberg, A., Sverdlov, Y. & Croitoru, N., Electroless silver and silver with tungsten thin films for microelectronics and microelectromechanical system applications. Journal of the Electrochemical Society, 147, 3345-3349 (2000));
2) laser ablation of metal films to create patterns;
3) laser direct writing based on pyrollitic deposition of metal from vapor, solution or solid precursors; (Auerbach, A., On Depositing Conductors From Solution With a Laser, Journal of the Electrochemical Society, 132, 130-132 (1985); Auerbach, A., Optical-Recording By Reducing a Metal Salt Complexed to a Polymer Host, Applied Physics Letters, 45, 939, 941 (1984); Auerbach, A., Copper Conductors By Reduction of Copper (I) Complex in a Host Polymer, Applied Physics Letters, 47, 669-671 (1985); Auerbach, A., Method For Reducing Metal-Salts Complexed in a Polymer Host WIth a Laser, Journal of the Electrochemical Society, 132, 1437-1440 (1985)); and
4) light exposure and development of silver-halide based photographic film followed by electroless and electrochemical plating (Madou, M. & Florkey, J., From batch to continuous manufacturing of microbiomedical devices. Chemical Reviews, 100, 2679-2691 (2000); M. Madou., Fundaments of Microfabrication (CRC Press, Boca Raton, 1997); Madou, M., Otagawa, T., Tierney, M. J., Joseph, J. & Oh, S. J., Multilayer Ionic Devices Fabricated By Thin-Film and Thick-Film Technologies. Solid State Ionics, 53-6, 47-57 (1992)).
Currently available methods are described, for example, in the following publications:
Southward, R. E. et al., Synthesis of surface-metallized polymeric films by in situ reduction of (4,4,4-trifluoro-1-(2-thienyl)-1,3-butanedionato) silver(I) in a polyimide matrix. Journal of Materials Research, 14, 2897-2904 (1999);
Southward, R. E. & Thompson, D. W. Inverse CVD, A novel synthetic approach to metallized polymeric films. Advanced Materials, 11, 1043-1047 (1999);
Gu, S., Atanasova, P., Hampden-Smith, M. J. & Kodas, T. T., Chemical vapor deposition of copper-cobalt binary films. Thin Solid Films, 340, 45-52 (1999);
Jain, S., Gu, S., Hampden-Smith, M. & Kodas, T. T., Synthesis of composite films. Chemical Vapor Deposition, 4, 253-257 (1998);
Gu, S., Yao, X. B., Hampden-Smith, M. J. & Kodas, T. T., Reactions of Cu(hfac)(2) and Co-2(CO)(8) during chemical vapor deposition of copper-cobalt films. Chemistry of Materials, 10, 2145-2151 (1998);
Calvert, P. & Rieke, P., Biomimetic mineralization in and on polymers. Chemistry of Materials, 8, 1715-1727 (1996);
Hampden-Smith, M. J. & Kodas, T. T., Chemical-Vapor-Deposition of Metals. 2. Overview of Selective CVD of Metals. Chemical Vapor Deposition, 1, 39-48 (1995);
Hampden-Smith, M. J. & Kodas, T. T., Chemical-Vapor-Deposition of Metals. 1. an Overview of CVD Processes. Chemical Vapor Deposition, 1, 8-23 (1995);
Xu, C. Y., Hampden-Smith, M. J. & Kodas, T. T., Aerosol-Assisted Chemical-Vapor-Deposition (AACVD) of Binary Alloy (Ag(x)Pd(1)-X, Cu(x)Pd(1)-X, Ag(x)Cu(1)-X) Films and Studies of Their Compositional Variation. Chemistry of Materials, 7, 1539-1546 (1995); and
Naik, M. B., Gill, W. N., Wentorf, R. H. & Reeves, R. R., CVD of Copper Using Copper(I) and Copper(II) Beta-Diketonates. Thin Solid Films, 262, 60-66 (1995).
The above described methods are limited to direct production of two-dimensional patterns, and three-dimensional patterns must be built up by use of multilayer or multistep processes. Laser direct writing of metal lines allows for single step microfabrication of one-dimensional or two-dimensional patterns, but has mainly involved thermal decomposition of a metal precursor at a high temperature created by absorption of laser energy. There is great interest in an ambient temperature process for forming metal lines by laser writing and for directly writing three-dimensional metal patterns.
Swainson et al., in a series of patents, (U.S. Pat. Nos. 4,466,080; 4,333,165; 4,238,840; and 4,288,861) described the photoreduction of silver by using conventional dyes such as methylene-blue and others as silver photoreducing agents in solution. Silver coatings of surfaces following optical excitation of such silver ion and dye solutions were described. The presence of “certain reducing/chelating agents, such as o-phenanthroline” were described as being a fundamental component of the system. Swainson also described that by following similar methods one would not be able to write continuous metal phases within a solid matrix. In fact, the introduction to the sections that included the metal photoreduction stated that the previously generally preferred stabilized or solid media are not suitable for the production of products with a material complexity above a certain level. Accordingly, their examples used gaseous and liquid physical states which according to Swainson permit increased complexity of products by virtue of their transportive capability. In the solid state, the present inventors have indeed found that Swainson's method does not result in the formation of continuous metal.
Whitesides et al. described a multistep method for the generation of conductive metal features both in an article: Deng T., Arias, F., Ismagilov, R. F., Kenis, P. J. A. & Whitesides, G. M., Fabrication of metallic microstructures using exposed, developed silver halide-based photographic film. Analytical Chemistry, 72, 645-651 (2000); and in U.S. Pat. No. 5,951,881. The key difference between the system described by Whitesides et al. and the system of the present invention is that they photochemically generate metal nanoparticles in a gelatin and in a subsequent step they use an electroless deposition of silver on the silver crystals, so as to develop it (Braun, E., Eichen, Y., Sivan, U. & Ben-Yoseph, G., DNA-templated assembly and electrode attachment of a conducting silver wire. Nature, 391, 775-778 (1998)), thus forming a continuous metal structure. Moreover, in order to obtain real 3D patterns they have to perform multi-step construction of the device. The smallest dimension of the lines (30 μm) described by Whitesides et al. is much larger than the one achievable with the method according to the present invention.
Reetz et al. described in an article and a patent titled: “Lithographic process using soluble or stabilized metal or bimetal clusters for production of nanostructures on surfaces” the fabrication via electron beam irradiation of continuous metal features starting from surfactant stabilized metal nanoparticles (Reetz, M. T., Winter, M., Dumpich, G., Lohau, J. & Friedrichowski, S. Fabrication of metallic and bimetallic nanostructures by electron beam induced metallization of surfactant stabilized Pd and Pd/Pt clusters. Journal of the American Chemical Society 119, 4539-4540 (1997); Dumpich, G., Lohau, J., Wassermann, E. F., Winter, M. & Reetz, M. T. in Trends and New Applications of Thin Films 413-415 (Transtec Publications Ltd, Zurich-Uetikon, 1998). Bedson et al., describe the electron beam writing of metal nanostructures starting from passivated gold clusters, that were alkylthiol capped gold nanoparticles. Bedson T. R., Nellist P. D., Palmer R. E., Wilcoxon J. P. Direct Electron Beam Writing of Nanostructures Using Passivated Gold Clusters. Microelectronic Engineering 53, 187-190 (2000)).
The differences between what is described there and the present invention are:
1) Reetz et al's and Bedson et al's processes involve fusion of nanoparticles rather than the growth of nanoparticles based on the generation of metal atoms upon excitation;
2) their starting materials are made solely of stabilized nanoparticles, whereas we teach the use of composite materials in which stabilized nanoparticles are just one of the components;
3) their irradiation method is solely electron-beam irradiation, while we teach that using suitable reducing agents our composite materials can be good precursors for a wide variety of stimulating radiation, electron-beams being just one of them; and
4) their nanoparticles are coated with ligands that provide only stabilization solubilization properties, while our compositions for electron beam patterning of metal are composites based on nanoparticles, metal salt, and an excited dye reducing agent, that can be included by covalent attachment to a ligand on the nanoparticle.
The compositions and methods of excitation of dyes with strong multiphoton absorption properties have been disclosed by Marder and Perry, U.S. Pat. No. 6,267,913 “Two-Photon or Higher-Order Absorbing Optical Materials and Methods of Use”.
Some compositions and methods have been disclosed for the multiphoton generation of reactive species including the photogeneration of silver particles in a patent application by B. H. Cumpston, M. Lipson, S. R. Marder, J. W. Perry “Two-Photon or higher order absorbing optical materials for generation of reactive species” U.S. patent application No. 60/082,128. The method taught in U.S. patent application No. 60/082,128 differs from those of this invention because in the prior application there is no mention of the use of metallic nanoparticles as precursors.